I prefer stainless reels because they use less chemistry (one shot), and are easier to load. Yes, easier.
Paterson is suitable only for three-armed aliens, because one needs two hands to hold the two reels, and a third hand to hold the cartridge. Stainless is easily loaded with just two hands (by humans).
Funny you should say that - I have two hands, years of developing experience and seem to manage well enough with plastic spirals with 120 and 35mm. In fact I've never used anything else. Here's a tip - you don't have to hold the cartridge/spool when loading a spiral...